Astrophysics > Cosmology and Nongalactic Astrophysics

Title:Scale-invariant alternatives to general relativity. III. The inflation--dark-energy connection

Abstract: We discuss the cosmological phenomenology of biscalar-tensor models
displaying a maximally symmetric Einstein-frame kinetic sector and constructed
on the basis of scale symmetry and volume-preserving diffeomorphisms. These
theories contain a single dimensionful parameter $Λ_0$-associated with
the invariance under the aforementioned restricted coordinate
transformations-and a massless dilaton field. At large field values these
scenarios lead to inflation with no generation of isocurvature perturbations.
The corresponding predictions depend only on two dimensionless parameters,
which characterize the curvature of the field--manifold and the leading order
behavior of the inflationary potential. For $Λ_0=0$ the scale symmetry is
unbroken and the dilaton admits only derivative couplings to matter, evading
all fifth force constraints. For $Λ_0\neq 0$ the field acquires a
run-away potential that can support a dark energy dominated era at late times.
We confront a minimalistic realization of this appealing framework with present
data sets. The impact of possible consistency relations among the early and
late Universe dynamics that could appear within this setting is also discussed.